The £100m tunnel, which will enable Scottish Water to improve water quality in the River Clyde and tackle flooding, will be 3.1 miles long, which is five times longer than the Clyde Tunnel.

The 1000 tonne, 180-metre-long tunnel started construction last July and is set to be completed later this year.

A full circle of giant concrete rings have been installed about 10 metres under the east of Pollok Park – the exact midway point of the tunnel.

Paul Kerr, Scottish Water’s capital investment general manager, said: “The Shieldhall Tunnel team includes some of the best and most experienced tunnellers in the world and they are making great progress with what is the biggest project of its type Scottish Water has ever undertaken.”

The tunnel is the biggest investment in the city’s waste water infrastructure in more than a century.